Thermal insulating of surfaces, for example in vehicles and buildings, has become widespread as a result of the growing request of humans for more living comfort, including a better temperature control of its direct environment, accompanied by a growing notion that the energy needed for said climate control is deemed to be scarce, and also contributes to the greenhouse effect, and therefore to the ecological footprint or carbon footprint of the user. Hence, for such reasons, there is a permanent request for reducing the necessary capacity to heat and/or cool the direct environment of humans, mainly in vehicles and buildings, mainly large buildings. such as office buildings.
Thermal insulating non-transparent parts of such surfaces, such as walls and partitions, has already become a standard practice in most circumstances. The energy exchange between the exterior environment with an interior environment, such as a passenger compartment of a vehicle, or the interior of a house, office or other building, occurs in most cases for by far the largest part through the transparent or translucent surfaces, such as through windows and other glazings.
For increasing the thermal insulation of glazings or other transparent surfaces, solutions have are already been offered, among which for example double or even triple glazing including one or more layers of air as insulation. In addition, this also offers an increased sound insulation, as well as a reduced risk for unwanted and possibly disturbing and/or detrimental condensation of moisture on the inside of the glass. However, these solutions are technically very radical and expensive in comparison with the nevertheless rather limited insulating effect achieved by it. Because the brightness of the view and the colour deviation of the transparent glazings is of primary importance, the insulating effect of those additional layers of glass is mainly achieved by reducing the heat conduction or conduction. The use thereof in vehicles is still uncommon.
It is found that, especially in vehicles and in buildings with large glass surfaces, still an undesirably high energy absorption may occur with a large incidence of sunlight, and alternatively, that an excessive high heat loss may occur from the inside to the outside at night, during the colder seasons, and through glazings with less or no incidence of sunlight. With the modern glazings, this energy exchange with the environment mainly occurs through radiation. This radiation energy occurs as visible light, in the relatively narrow visible range of wavelengths of about 380 to about 780 nanometer (nm), but also as ultraviolet (UV) radiation in the range of the shorter wavelengths of 280 to 380 nm and as infra-red (IR) radiation in the even wider range of the longer wavelengths up to about 1 mm.
Still, there remains the need to make transparent or translucent surfaces even more energy-shielding, such as glazings, mainly by influencing the radiation energy transmitted through such surfaces. It is thereby often undesirable that this should occur at the expense of a considerable reduction of the visible light that is been transmitted, mainly from the outside to the inside, for example in order to need to use less artificial light during daytime, or of an important change of the colour perception through such surfaces, as this is less appreciated by the user.
To make translucent surfaces, such as glass, more energy-shielding, energy-shielding plastics films have been developed, which try to absorb as selectively as possible the radiation from the range, not visible to the eye, but either the detrimental UV (A&B) range or the heat-generating IR (A, B &C) range. The infra-red radiation range is commonly divided into, on the one side, the near-infrared radiation range, N-IR or IR A&B, up to a wavelength of about 2500 nm, and the long-wavelength IR range, covering the range to 50,000 nm or 50 μm, and according to some authors up to and including 1 mm. Since solar radiation carries a lot of radiation energy with wavelengths in the near-IR range, technological improvements have mostly focused thereon. Hence, films have been developed which have a better infra-red absorption function, which provides a more even heat distribution and a more pleasant interior temperature at a high incidence of light. A disadvantage of these films is that the absorbed radiation is converted into heat in the film. Hence, this absorption may cause local temperature increases, which are passed on onto the substrate on which the film has been applied. With many substrates, such as glass, such local temperature increases lead to a high stress, and even may lead to glass breakage. A second disadvantage is that the absorbed heat, although transmitted to the interior in a more evenly manner, may still also locally cause a considerable temperature increase, which may still be perceived as unpleasant. Furthermore, transmission of this heat to the air leads to a loss of efficiency.
Hence, a high absorption of the incident solar energy does not lead to uncomplicated solutions. To limit or avoid these disadvantages as much as possible, films were developed with IR-reflecting properties, especially aimed at reflection in the near-IR radiation range. These films offer a reduction of the heat absorption of a vehicle or building equipped therewith in summer, such that cooling energy may be saved.
U.S. Pat. No. 6,797,396 describes a film transparent for visible light but reflecting infra-red light, and made from different polymer layers and which is metal-free. US 2008/0292820 A1 describes a multi-layered polymer film which has a haze value of at least 10% to further also control the sun-shielding properties by light diffusion. Metals may be incorporated in several successive metallic layers in the film, and they will cooperate as a Fabry-Perot interference filter to reflect the IR light and/or especially the so-called near-IR light. This is because solar radiation mainly appears in a wavelength range from 280 nm to 2500 nm. Until now, little or no attention has been given to the activity of long wavelength IR-C radiation energy.
US 2005/0134959 describes a UV-screening film which also reflects electromagnetic radiation, comprising a layer of silver. Additional layers may serve as a protective layer for the silver or may provide additional anti-reflection properties. Also WO 2007/009004 describes a film for screening electromagnetic radiation, comprising some metal and/or metal oxides. On the other hand, transparent semiconductors have been described as usable for saving energy, such as by C. Grandqvist, Transparent conductors as solar energy materials: A panoramic view, published in Solar Energy Materials and Solar Cells, Elsevier Science Publishers, Amsterdam, Part 91, 3 Jul. 2007, pages 1529-1598. However, the thickness of the layers used is still rather high. However, none of these documents mentions the use of antimony and/or arsenic in these applications.
However, the inventors have determined that, until now, a high degree of reflection has always been accompanied by a rather high degree of absorption, and that these reflecting films nevertheless still heat up by a rather high absorption of radiation energy. Although these films try to reflect as much radiation as possible, mainly in near-IR range, there is still a too high degree of absorption present in said range but also in the UV and in the long wavelength IR range, and as such, the problem of local heating associated therewith is still far from being solved.
For this reason, there remains a need for energy-shielding plastics films which reflect well, but at the same time heat up less by the incident radiation, and by the radiation energy absorbed there from over the full radiation range.
The object of the present invention is to reduce of solve the aforementioned problems, and/or to teach general improvements.